Turbine by-pass arrangement for thermal power plants

ABSTRACT

A turbine by-pass arrangement for use in thermal power plants serves to by-pass a portion of the steam delivered by the steam generator around the turbine and discharge it into the coupling sleeve located between the turbine outlet and the condenser inlet. The by-passed steam is divided into two parts, one of which is de-compressed as well as de-superheated while the other part is merely de-compressed. The two parts are admitted into the coupling sleeve in such manner that each constitutes a screen with respect to the other as regards protection for the turbine and condenser components of the installation.

United States Patent Lecocq Nov. 18, 1975 TURBINE BY-PASS ARRANGEMENT FOR 3.364.125 H1968 Switzer .1 60/657 x THERMAL POWER PLANTS 37507395 8/1973 Tapper et a1. 60/690 [75] Inventor: FrancoisLecocq, Fontenay aux FOREIGN PATENTS OR APPLICATIONS Roses, France 447.350 12/1912 France 60/690 [73] Asslgnee: g i gg Boyer & Company Primary E.\'aml'nerMartin P. Schwadron Assistant E.\'t1minerH. Burks, Sr. [22] Filed: Dec. 18, 1973 Attorney, Agent, or Firm-Pierce, Schefflcr & Parker [21] Appl. No.: 425,843 [57] ABSTRACT A turbine by-pass arrangement for use in thermal Forelgn Appllcatloil y Data power plants serves to by-pass a portion of the steam Jan. 2, 1973 France 73.00039 delivered y t st am gen rat r around th tur in and discharge it into the coupling sleeve located be- [52] US. Cl. 60/657; 60/690; 60/693 een the urbine outlet and the condenser inlet. The [51] Int. Cl. F01k 17/04; FOlk 9/00 by-p sed steam is divided into two parts, one of [58] Field of Search 60/653, 657, 685, 690, which is de-compressed as well as de-superheated 60/64, 65 while the other part is merely de-compressed. The two parts are admitted into the coupling sleeve in such [56] References Cited manner that each constitutes a screen with respect to UNITED STATES PATENTS the other as regards protection for the turbine and 1,080,734 12/1913 Thomson v. 60/657 Condenser Components of the mstallatlon' 2.811837 1 H1957 Eggenberger 60/657 X 9 Claims, 1 Drawing Figure US. Patent Nov. 18, 1975 w HH H j TURBINE BY-PASS ARRANGEMENT FOR THERMAL POWER PLANTS The present invention relates to an improvement in a steam-turbine by-pass arrangement between the steam generator and condenser in a thermal power plant.

Conventionally, steam-turbine thermal power plants provide a by-pass arrangement so as to directly connect the steam generator to the condenser, so that excess steam, upon disconnection of the network supplied by the turbo-alternator group, or upon any sudden decrease in load, also upon starting the turbo-alternator group and its rise in output, will be directed toward the condenser. The flow rate being applied directly to the condenser through the by-pass may therefore vary within fairly wide limits.

The flow rate allowed in the by-pass pipes under consideration is selected as a function of the admissible amounts which may be expelled into the atmosphere through the safety valves of the steam generator. Clearly it is costly to expel large amounts of steam since their replacement requires introduction of fresh water and treatment by conventional processes, and there is interest in properly scaling the bypass arrangement, which is costly, following a suitable cost-analysis.

As regards the nuclear power plants, the difficulty of the problem is compounded because on one hand the by-pass pipes may be constantly in use for a long time prior to starting the turbo-altemator group and on the other hand, when there is disconnection, the inertia of a steam generator used in nuclear power plants is much larger than that of a fossile fuel generator.

The following conditions must be observed when dealing with by-passes of large flow rates: on one hand, there must be no deterioriation in the low-pressure part of the turbine or of the flexible seal between turbine and condenser, a certain temperature, for instance 80C, may not be exceeded, and on the other hand, one must avoid having water droplets passing through the by-pass and arriving at high speed in the expanding steam at the entrance of the condenser, there being the danger of these drops eroding the condenser tubing.

These two conditions sometimes are difficult to meet, particularly when all of the generator output passes through the by-pass pipe, the output therefore being larger than the normal escape flow rate.

In order to achieve proper expansion/de-superheating, an enclosure with a pressure corresponding to a sufficiently low temperature, for instance 80C, must be available, which, in view of its bulk and the difficulties in joining large ducts, must be placed within the condenser. The desuperheated steam inlets will appropriately be of large cross-sections so that the entrance speed in the condenser will be low enough to avoid any danger of erosion on the part of the water drops.

In order to eliminate the drawback of such large enclosures, suggestions have been advanced to admit non-desuperheated steam at 140C directly underneath the cluster of condenser tubes, but this is feasible only for low flow rates and for favorable condenser installations.

The present invention is directed to achieving simultaneously good de-superheating at low pressure and a reduction to a tolerable value with respect to the condenser tubes of the stopping pressure of the jets bringing the de-superheated steam toward the condenser cluster. To that end, the present invention proposes a division of the by-pass steam arriving above the condenser tube cluster into two parts: one part of the flow is properly decompressed and de-superheated and, following water separation, the temperature-lowered steam will be de-compressed again in stages and introduced, on the turbine-side, into the coupling sleeve between the low-pressure turbine and the condenser; a second part of the flow is de-compressed in stages but not de-superheated and this part will be applied to the condensation region at a higher pressure, but lacking water drops, it may be admitted into the coupling sleeve between turbine and condenser on the side of the latter, above the tube cluster and below the first flow or flux. When this arrangement is obtained, the de-superheated steam constitutes on one hand a thermal screen protecting the turbine from the nondesuperheated steam, while on the other hand, the nondesuperheated steam, to which has been admixed the de-superheated steam following elimination of the large water drops, constitutes a kind of screen protecting the condenser tubes from those water drops. The ratio of the flow rates of these two parts of the flux may be suitably selected to obtain a minimum cost of the set of the two pressure reducer-desuperheaters and pressure reducer, the latter being of much lesser bulk for the same output.

The above relates especially to a nuclear power plant, but it applies equally well to a fossil fuel station of which the operational cycle requires frequent use of the by-pass pipes.

An example of an installation in conformity with the invention is shown in schematic form in the attached drawing:

As illustrated the low-pressure part 1 of the turbine is coupled by flexible seal 2 to the sleeve of the condenser 5 which comprises an upper region 3 at the side of the turbine and a lower region 4 at the condenser side schematically bounded by the dot-dash lines; condenser 5 comprises cooling boxes 6 and 7, the tube cluster 8 and well 9, of which the outlet orifice toward the evacuation pump of known design is not shown.

The steam coming directly from the steam generator, 'e.g. a boiler not shown, arrives through the by-pass pipe 10 which, in conformity with the invention, is divided into two parts by branch conduits 11 and 12, that part of the steam passing through conduit 11 and its regulating valve 13 arriving through a divergent pipe where it experiences a first expansion at the de-superheater, water injector 14, the de-superheating water coming through conduit 15 which is controlled by regulating valve 16. The desuperheated and initially decompressed steam then penetrates enclosure 17 in the upper region 3 of the condenser sleeve adjacent the turbine discharge outlet, where water separator 18 is located, which is of known design. Entry into enclosure 17 may be achieved through a perforated plate 19 (or any other suitable device) allowing the excess water to atomize. Pressure reduction staging is achieved in that steam passage from separator 18 to the upper region 3 of coupling sleeve occurs through large orifices such as 20, 21 and through intermediary cases such as 22 where the steam experiences a series of pressure reductions of which the number is determined by the overall geometry of the enclosures of the apparatus. In conformity with the invention, the pressure in region 3 of the sleeve and for steam by-passing will have been sufficiently lowered so that there will be no danger of eroding the condenser tubes, and the corresponding low- 3 cred temperature will pose no danger to either the lowpressure part of the turbine or to the flexible joint between turbine and sleeving. The separated water will drain through a suitably arranged pipe system 27 in the condenser.

That part of the steam passing through conduit 12 and its regulating valve 23 will be successively pressure-reduced, but without there being any de-superheating, in a case 24 where it arrives through a number of perforated pipes 25 of which only one is shown for the sake of clarity. This case is provided with a series of apertures 26 located in such manner that they force the steam to move in a different direction. These apertures ensure the second decompression affecting pressure only and communicate with the lower region 4 of sleeve at the condenser inlet where its stopping pressure is considerably reduced. The space required by case 24 is much less than that for cases 17 and 22 since there is no danger that the steam will act as a vehicle for water drops that might erode the tubes or the walls. The dry steam arriving in a region below that where the steam is desuperheated, will shield the condenser from the water drops which necessarily are located in the latter region. inversely, the steam located in the upper region being of lower temperature will act as a screen with respect to the low pressure stages of the turbine and of the flexible seal between turbine and condenser, which are in no danger of being raised to excessive temperatures.

I claim:

1. In a thermal power plant including a steam generator supplying steam to a turbine and wherein steam exhausted from the turbine is passed through a coupling sleeve connecting the turbine outlet with the inlet of a condenser and thence returned as condensate to the steam generator, the improvement which comprises means for by-passing steam around the turbine in two parts, means for decompressing and also desuperheating one such part of the by-passed steam, means for decompressing but not desuperheating the other such part of the by-passed steam, means for introducing the decompressed and desuperheated part of the steam into said coupling sleeve at the turbine outlet side thereof and means for introducing the decompressed and non-desuperheated part of the steam into said coupling sleeve at the condenser side thereof whereby the desuperheated part of the steam protects the turbine against the nondesuperheated steam part and the nondesuperheated steam part protects the condenser against any water droplets which may escape into the coupling sleeve from the desuperheated steam part.

2. A steam turbine by-pass arrangement as defined in claim 1 wherein desuperheating of one of the steam parts is effected by means injecting water into the steam skid injecting means being followed by a device for water drop separation.

3. A steam turbine by-pass arrangement as defined in claim 1 wherein means are provided for reducing the pressure of the steam in each part in a plurality of partial de-compression stages.

4. A steam turbine by-pass arrangement as defined in claim 1 wherein the ratio of the two parts of the bypassed steam is adjustable.

5. A steam turbine by-pass arrangement as defined in claim 1 wherein the ratio between the two parts of the by-passed steam is fixed.

6. A steam turbine by-pass arrangement as defined in claim 1 and which further includes self-adjusting valves for controlling the amount of steam in each part that is admitted to said coupling sleeve.

7. A steam turbine by-pass arrangement as defined in claim 1 wherein at least one of said means for decompressing and desuperheating one part and said means for decompressing the other part of the by-passed steam are at least partially located in said coupling sleeve.

8. A steam turbine by-pass arrangement as defined in claim 7 wherein at least one of said decompression and said decompression and desuperheating means comprise a plurality of sections operating in parallel.

9. A steam turbine by-pass arrangement as defined in claim 1 wherein said means for decompressing and desuperheating one part of the by-passed steam includes a valve, a divergent pipe, a water injector, a water separator and a succession of decompressing means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,919,846

DATED Nov.18,l975

INVENTOR(S) Francois Lecocq It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In claim 2, line i "skid should read said a I I Signed and Sealed this sixteenth Day-of March 1976 [SEAL] O Attest:

RUTH c. MASON c. MARSHALL DAN-N A res ing Offic Commissioner oj'Parents and Trademarks 

1. In a thermal power plant including a steam generator supplying steam to a turbine and wherein steam exhausted from the turbine is passed through a coupling sleeve connecting the turbine outlet with the inlet of a condenser and thence returned as condensate to the steam generator, the improvement which comprises means for by-passing steam around the turbine in two parts, means for decompressing and also desuperheating one such part of the by-passed steam, means for decompressing but not desuperheating the other such part of the by-passed steam, means for introducing the decompressed and desuperheated part of the steam into said coupling sleeve at the turbine outlet side thereof and means for introducing the decompressed and nondesuperheated part of the steam into said coupling sleeve at the condenser side thereof whereby the desuperheated part of the steam protects the turbine against the nondesuperheated steam part and the non-desuperheated steam part protects the condenser against any water droplets which may escape into the coupling sleeve from the desuperheated steam part.
 2. A steam turbine by-pass arrangement as defined in claim 1 wherein desuperheating of one of the steam parts is effected by means injecting water into the steam skid injecting means being followed by a device for water drop separation.
 3. A steam turbine by-pass arrangement as defined in claim 1 wherein means are provided for reducing the pressure of the steam in each part in a plurality of partial de-compression stages.
 4. A steam turbine by-pass arrangement as defined in claim 1 wherein the ratio of the two parts of the by-passed steam is adjustable.
 5. A steam turbine by-pass arrangement as defined in claim 1 wherein the ratio between the two parts of the by-passed steam is fixed.
 6. A steam turbine by-pass arrangement as defined in claim 1 and which further includes self-adjusting valves for controlling the amount of steam in each part that is admitted to said coupling sleeve.
 7. A steam turbine by-pass arrangement as defined in claim 1 wherein at least one of said means for decompressing and desuperheating one part and said means for decompressing the other part of the by-passed steam are at least partially located in said coupling sleeve.
 8. A steam turbine by-pass arrangement as defined in claim 7 wherein at least one of said decompressIon and said decompression and desuperheating means comprise a plurality of sections operating in parallel.
 9. A steam turbine by-pass arrangement as defined in claim 1 wherein said means for decompressing and desuperheating one part of the by-passed steam includes a valve, a divergent pipe, a water injector, a water separator and a succession of decompressing means. 